Self-purging hydraulic cylinder



Feb. 24,1970 c. A. BARRETT ET AL. 3,496,838

- SELF-PURGING HYDRAULIC CYLINDER Filed May 15, 1967 2 Sheets-Sheet 1 /9 R lllllll l/Il/l/l/l INVENTORS (206/4 54.616577" MM ZMWM ATTOR'NEYS Fe 24,10 BARRETT ETAL SELF-PURGING HYDRAULIC CYLINDER Filed May 15, 1957 2 Sheets-Sheet 2 INVENTORS fle/c/4 692,657;-

BY I

ATTORNEY United States Patent 3,496,838 SELF-PURGING HYDRAULIC CYLINDER Cedric A. Barrett, Grand Rapids, and James J. Newell,

Comstock Park, Micln, assignors, by mesne assignments to Pall Corporation, Glen Cove, N.Y., a corporation of New York Filed May 15, 1967, Ser. No. 638,439 Int. Cl. Fb 21/04, 15/22 US. Cl. 9279 2 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a self purging power cylinder or motor particularly useful as a power cylinder in, for example, dies and of particular utility where the cylinders or hydraulic motors are positioned vertically so that their pistons extend upwardly and hence provide pockets behind the piston for the collection or accumulation of air or gas. Not unusually the gas or air so pocketed substantially interferes with the performance of the piston and the circuit in which the piston is a part since the gas is compressible and the hydraulic fluid is relatively incompressible.

In the prior art it is customary to utilize bleeders or channels from the highest entrapment points in an hydraulic device for removal of accumulated gas or air. Bleeding of the lines in such instances usually involves opening the bleeder until hydraulic fluid appears and then closing the channel as by a small petcock or valve or by use of a simple plug. In many applicaions of pistons and their cylinders this bleeding is diflicult to accomplish unless the channel is axially through the piston. In the use of power cylinders in dies and tools the cylinders are usually inaccessible and the pistons and cylinders are diflicult to bleed, not unusually requiring dismantling of the tools, dies or fixtures in which they are integrated. Hydraulic cylinders are known to characteristilly trap compressible gases which are troublesome to the entire circuit function. In such hydraulic applications the liquid or hydraulic fluid sometimes carries entrained or generated vapor, gas, or air and in such situations the entrapment of the gaseous material beneath the piston provides a continous, rather than intermittent, source of difliculty.

Such problems require means that initially and continuously purge the cylinders of entrapped air and preferably without extensive modification of the piston base. In the United States Letters Patent 2,924,446 a recess is required extending upwardly and axially into the piston. The recess in the piston cooperates with a fluid conducting tube extending upward axially from the fluid connection of the cylinder. This system for purging actually provides two traps for gases or air. One is in the recess provided in the piston and the other is the area adjacent the piston base. By contrast, in the present invention, a flanged purging element is secured to the base of the piston and depends therefrom. As the piston reciprocates, entrapped gaseous materials are continuously entrained with the hydraulic fluid and are flowed out of the cylinder and into the hydraulic lines. The gaseous material, thus collected, is radially fed through a flange plate and exhausted in the main stream flow line. In the flow process the gas is dispersed in the liquid and the currents set up in the cylinder sweep the cylinder free of the dispersed gases. No machining is required in the sump portion of the cylinder and the clearance relationship of the flanged purging element does not interfere with the function of the power piston.

GENERAL DESCRIPTION In general, a flanged tubular purging element is provided which is coaxially secured to the base of a piston. The flanged portion bears on a cup type gasket and sandwiches the gasket between piston base and flange and the tubular portion of the purging element depends axially from the flanged portion. The flanged portion has a diameter substantially less than the base of the piston. The flanged portion is radially penetrated to communicate with the axial opening of the tubular depending portion. The tubular depending portion is also radially perforated adjacent its lower opening. The cylinder, into which the piston is inserted is provided with a sump. The sump is of a diameter greater than the tubular depending portion of the purging element and an hydraulic port for oil ingress and egress to the cylinder radially communicates with the sump. The depth of the sump is slightly greater than the length of the depending tubular portion of the purging element.

Gaseous materials collect in the cylinder immediately beneath the piston. As the piston is depressed the gaseous materials trapped between the piston and the hydraulic fluid flow through the radial flange openings and downwardly through the tubular depending portion followed or admixed with a cascading flow of hydraulic fluid exhausting partially through the same radial passage and flow of the fluid is exhausted into the sump and into the external hydraulic lines. Ultimately, the gaseous material flows back to tank where it is separated as by a gas over oil separation system. Observed through clear plastic cylinder walls the scouring out of the gaseous material is eflicient and the piston action is unimpaired. The sweep ing action seems to break the gas into tiny bubbles which are easily carried away in the stream of hydraulic fluid. Hence, gases are accumulated adjacent the base of the piston and as the piston reciprocates the gases are driven radially to an axial position beneath the piston and dispersed and driven by the following hydraulic fluid and entrained therein to be swept out of the piston and into connecting hydraulic conduit.

The self purging structure is useful wherever hydraulic power cylinders or motors are used but is particularly advantageous in hydraulic circuits where the pistons are integrated into tools, dies, or fixtures to perform work such as in holding, forming, stripping or punching and where the piston is uppermost. As will be appreciated purging is less of a problem where the piston is oriented downwardly from the cylinder but even in such situations the sump and purging device herein described cooperate to exhaust gaseous material from the cylinder.

In the drawings:

FIGURE 1 is a perspective view of a self purging cylinder and piston in accord with the present invention and shown with the piston sligthly extended and with an hydraulic line radially extending from the cylinder.

FIGURE 2 is a top plan view of a cylinder and piston in accord with the present invention.

FIGURES 3, 4 and 5 are cross section views taken on the line IIIIII of the FIGURE .2 and indicating the operation of the purging structure where FIGURE 3 shows the piston fully extended, FIGURE 4 shows partial depression of the piston, and FIGURE 5 shows complete depression. From these FIGURES 3, 4 and 5 the sequence through a full piston cycle is indicated and the sweepingpurging action is best understood.

FIGURE 6 is a partial cut-away elevation view showing a purging piston and cylinder in accord with the present invention in a forming die with the piston extended to support a cushion ring and connected to a typical press cushion circuit.

FIGURE 7 is a perspective view of one form of the flanged tubular purging element.

FIGURE 8 is a perspective exploded view of another adaptation of the flanged tubular purging element and indicating the simplicity of the structure.

SPECIFIC DESCRIPTION Referring to the drawings and specifically to FIGURE 1 thereof a self purging cylinder and piston 11 is shown. The cylinder 12 is a tubular receptacle axially receiving the piston 13. The cylinder 12 is connected to an hydraulic line 14. As pressure is applied to the piston 13 it moves axialy into the cylinder 12 and hydraulic fluid is displaced from the cylinder 12 and into the line 14. When pressure on the piston 13 is less than the pressure on the piston from the line 14, then the piston 13 extends as shown. Work may be performed during the depression of the piston 13 as by use of the resistance force as in holding, or during extension of the piston, as in stripping, or in both directions as by forming and stripping in sequence. While the style of the cylinder 12 is shown as flanged it will be appreciated that other styles of cylinders 12 are encompassed within the scope of the present invention. Inside the cylinder 12 the self purging structure will be seen. In FIGURE 2 the self purging piston and cylinder 11 is seen in top plan view and the internal structure is revealed in the operational sequence of FIGURES 3, 4 and 5. The piston 13 is seen as a cylindrical metal plug movable in the tubular cylinder 12. As previously indicated, the flange 15, may or may not be a part of the cylinder depending upon the particular installation desired. The piston 13 is coaxial with the cylinder 12 and the fit is close as between the wall of the cylinder 12 and piston 13. Seal is accomplished as by ring seal 16 and cup packing 17. Together these seals 16 and 17 assure that hydraulic fluid under operating pressures is retarded from escape around the piston 13. Depending from the base 18 of the piston 13 and coaxial with the piston 13 is a flanged purging structure 19 comprising an upper flange extension portion 20 and a tubular axially depending portion 21. The flanged purging structure 19 is secured to the base 18 of the piston 13 as by the screw 22 or other suitable fastening means. The diameter of the flanged portion 20 is less than the diameter of the piston base 18 and the flange portion 20 compresses the cup gasket firmly against the base 18 of the piston 13. In pistons using other types of seals the flanged purging structure 19 is directly attached to the piston base, the flange portion 20 is in flush parallel relation to the base of the piston. Radial openings 23 are provided in the flange portion 20 converging on and communicating with the axial tubular opening 24 in the tubular depending portion 21 of the self purging structure 19. Proximate the lower open end of the tubular portion 21, additional radial openings 25 are provided.

The cylinder 12 is otherwise conventional in form but includes a depression or sump 26 having a slightly larger diameter than the tubular depending portion 21 of the flanged purging member 19. The sump 26 is provided on the cylinder axis so that as the piston 13 is depressed the tubular portion 21 drops into the sump 26. As will be seen a clearance is provided as between sump 26 and tubular portion 21 in all positions. The hydraulic line 14 is connected to communicate in flow relation with the sump 26. In the FIGURE 3 the piston 13 is fully elevated or extended and an exaggerated interphase between liquid and gaseous phase materialsis indicated. Partial depression is indicated in FIGURE 4 and the gaseous material has passed from the cylinder 12 and has been urged by the hydraulic fluid downward in the tube portion 2]. of h urging device 19. The otal volume of the gase us materials has been broken to bubbles, empited into the sump 26 and forced out the port or conduit 14 entrained in the exhausting hydraulic fluid. In FIGURE 5 the piston 13 is shown substantially fully depressed and the hubbles of gaseous materials have been substantially evacuated and entrained in the exhaust hydraulic fluid. After several pumping strokes all gaseous materials have been driven from the cylinder 12 and as gases tend to accumulate they are likewise pumped from the cylinder 12 by the action induced by the purging structure 19.

In FIGURE 6 the cylinder 12 including piston 13 as located in schematized die or press structure 33 and the conduit 14 is shown connected to a typical resistance control and return circuit which includes an air-over-hydraulic tank 27. The control valving 28 includes a pressure relief valve which can be set to open at any selected pressure and a check valve 30' which blocks flow to the tank 27 from the cylinder 12 but allows return flow from the tank 27 to the cylinder 12. The check valve 30 is positioned in the line 31 around the pressure relief valve 29 in the line 32. As is well known in the art a wide variety of pressure relief valves are available, for example pilot operated and with or without sequencing attachments. Similarly the check valve 30 may be of the retard or delay release type and timed to the press movement or die position. The air return pressure may be augmented by power boosters. While the self purging structures 11 find principal application in the circuits as represented in FIGURE 6, they also are useful in hydraulic press and pump circuits whereaver a purging problem exists.

By reference to the die structure 33, the cylinder 1-2 is shown secured in the pad element 34 and the piston 13 extends up to engage the ring 35. These elements are related to the lower portion of the die structure 33 as shown. The work piece 36 is indicated as clamped by die element 37 and die ring piece 38 is positioned preparatory to forming the work piece 36 during which movement the piston 13 will be depresed. Maximum utility for the self purging cylinder structure 11 is indicated in the FIGURE 6 but as previously indicated the purging units 11 are useful in any hydraulic cylinder settings where purging is required and may be adapted to double acting pistons or free piston situation well known in applied hydraulics.

FIGURE 7 shows the flanged purging structure 19 isolated from the piston to which it is attached in use. The flange portion 20 includes the radial converging openings 23 in communication with the tubular coaxial portion. The lower radial openings 25 through the walls of the tubular portion 21 assure maximum flow relations of the tubular portion 21 where it enters the sump 26 (FIGURE 3). The axial opening 39 provided through the flange portion 20 provides means to fasten the purging element 19 to the base of a piston, as by the screw 22 (FIGURE 3 While the FIGURE 7 expresses a substantially integral form of the purging structure 19, except as the tubular portion 21 may be welded, brazed, or threadably engaged with the flange 20, the FIGURE 8 device is a modified composite in form of the purge structure 19'. In this structure 19' the openings 40 are milled as grooves and are then closed by the plate cap 41 secured to the flange 42 as by the recess headed screws 43. The tubular portion 44 may be made integral with the flange 42, or as previously indicated may be coaxially secured thereto as by brazing, welding, or threading. The axial center opening 45 in the plate cap 41 accommodates the screw 46, accessible through the tube 44 for attachment to the base of a piston (not shown). Here, the milled or otherwise provided radial openings 40 are easily modified in size to adjust to particular flow or pressure conditions encountered or desired in particular cylinders, and usually a function of size of cylinders and accommodated pistons. In some installations the form of the device 19' is used without the plate cap 41 and in such instances the screws 43 are passed upward through the opening 47 to sec re the flange 42 directly to the base of the piston. Radial openings 48 are provided through the wall of the tube 44 adjacent the lower end thereof.

It will also be appreciated that is some installations, as where the cylinder is secured to a manifold, that the depending tubular portion 21 or 44 is extended directly into the manifold conduit and in such instance the manifold becomes the sump.

OPERATION Devices in accord with the present invention were observed in operation in clear resin or plastic and within several strokes all observable accumulations of gaseous material were purged from the cylinder and into the feeder lines for ultimate separation at the accumulator tank provided with an air-fluid interphase. Where such tanks are not available the air bubbles may be accumulated and bled from the lines in a well known manner. The purge units herein described scrub the air or gaseous material from the operating cylinders and appear to break the masses of accumulated air into a fiowable dispersion of minute bubbles in the hydraulic fluid. Characteristic sponginess of the system is removed quickly by the consequent pumping action induced in the cylinders.

We claim:

1. A hydraulic cylinder structure for purging gases therefrom comprising:

a cylinder having at least one coaxial tubular piston recess, at least one port defined through the walls of said cylinder, and including a sump depression in the wall of said cylinder positioned coaxially with said piston recess, the bottom of said sump con1- municating to said port;

a piston having a substantially flat base mounted for a flanged hollow tubular purging element depending axially from the base of said piston, the flange portion thereof being coaxially rigidly secured to said piston base by fastening means and including radial openings adjacent the base of said piston and in open communication with the tubular portion thereof, and

said hollow tubular portion having a diameter less than the width of the sump depression so that said elemerit is movable in clearance relation into and out of said sump with axial movement of said piston, whereby gases are entrained and dispersed in hydraulic fluid and swept from said cylinder. 2. A hydraulic cylinder structure as claimed in claim 1, wherein there are additional radial openings adjacent the tip of the purging element, said radial openings being in communication with said hollow center of said element.

References Cited UNITED STATES PATENTS MARTIN P. SCHWADRON, Primary Examiner IRWIN C. COHEN, Assistant Examiner reciprocal movement in said tubular piston recess of 5 said cylinder; and

US. 01. x11, 

